Process and means for producing metallic cyanids



Patented Sept. 7, 1920.

. HIDDEN.

Princess AND MEANS Fon rnooucme METALLIC cYANms. APPLICATN FILED NV|18| |918. 1,352,192.

UNITED STATES PATENT OFFICE.

CHARLES P. HIDDEN, OF PROVIDENCE, RHODE ISLAND, ASSIGNOR TO NITROGEN PROD- UCTS COMPANY, OF PROVIDENCE, RHODE ISLAND, A CORPORATION OF :RHODEV ISIAND.

PROCES$`AND MEANS FOR PRODUCING METALLIC CYANIDS.

Specilcation of Letters Patent.

Patent-ed Sept. 7, 1920;

Application filed November 18, 19'18. Serial No. 262,925.

To all! 1f/wm it may concern:

Be it known `that I, CHARLES P. HIDDEN, a citizen of the United States, residing at Providence, in the county of Providence and State ol Rhodev Island, have invented certain new and useful Improvements in Processes and Means for Producin Metallic Cyanids, of which the following is a specification.

This invention relates to a process and means for producing alkali metal cyanide and hasfor one of its objects the effecting of a nitrogen fixing reaction in which are ticipatc the nitrogen -toy be fixed, sodium carbonate or the like and carbon, in such manner that a more copious yield of the product resulting from such reaction, may be obtained.

In the patent to John E. BucheigrNo.`

1,120,682, dated December 15, 1914, there is described a process for producing cyanid through the intcrmediaey of such a reaction; the operation Apreferably being conducted continuously in a vertical retort or the like. p

In said Bucher process a preferred mode of conducting the operation involves forming an intimate mixture of finely divided iron, sodium carbonate and powdered coke, for example, and then briqueting said mixture, in order that the charge treated in the retort may be suiliciontly open in structure to permit ol the free passage 'of nitrogen therethrough.

These briquets are themselves porous, so that the nitrogen current is thereby enabled to gain free access to the interiors thereof, and when said briquets have been heated 'to a reacting temperature, sodium cyanid, for example, will he AFormed according to the equation:

As the herein described process, in one of its aspects constitutes an iin rovement upon said process pf John Buc er,^it will suflice, for present purposes, to direct the attentifrn of those skilled in the art to the -dethe drawin which forms a part hereof; like reference ciaracters refer-rin to like parts in the respective, views.V As, various changes which Amay be made in the process herein described and in the apparatus,K given by Way of exeinplcation, ,in which said process may be eiiectuated, I desire to be limited only by the scope of the `section 2, and the latter in turn into the lower or cooling section 3; the joints being Welded gas tight.

rickwork Il is disposed to provide a conduit uthrough which the heating gases are led into the retort chamber 6, and thence out via a flue 7, as per the arrows.

At the top of the section 1 is a hopper 8 through which the briquets 9 are fed into the retort; While a suitable feed mechanism in a casing 1() receives and removes from the cooling section 3, the material produced by the cyanizing operatipn.

The specific construction of mechanism in the casing 10 docs not concern the present invention and hence need not hereinibc further referred to.

The orifices in th'e brickwork through which the retort is -introduced, are sealed -subi-:tantially gas tight, as by kieselguhr 11 means of packing 14 and al packing ring 15.

The upper end of seetionl preferably extends up through and somewhat beyond the top of thefurnace, and may be heat insulated, as at 16, for reasons hereinafter set forth.

Into the upper end of the retort is inserted a relatively small pipe 17, througl'l which preheated carbon mnoXid,-mixed or unmixcd with nitrogen, but preferably substantially pure-s introduced into said upper end of the retort; pipe 17 being, de-

am aware of' tends to form in zone a in the presence of its high content of CO, While much of the cya` nid which volatilizes in lower zonesand escends far as zone a, is, indeed, reconverted backto carbonate.

Any eyanid which happens to pass unQ changed through zone a, is in any case promptly converted to carbonate at the base of the column of relatively cool briquets immediately thereabove, Where the temperature is much lower and hence favorable to the reaction as per equation 2; This is proven by the formation of the crust of sodium carl honate just above zone a, in the batch furnace operation.

' Now, since the cyanid tends to more or less slowly volatilize from all of the zones, a, b, c, etc., andesgecially from the hotte;` ones, it is evident t at' in such hotter `zones it will volatilize most rapidly when its vapor ressure is. lowest. This is, of course, in the )ottom zones, since While this is slightly cooler than zoned, the latter receives vaporous cyenid from e, which tends to prevent excessive volatilization from d until e has been largely exhausted of cyanid,Y after which al will become the zone from which vmigration of the alkali metal in theform of its cyanid, will most copiously occur; and so on.

In other Words, it, a charge such as that in question, be treated long-enough in a batch furnace, it is possible to remove praetieally all alkali metal' from zones b, c, d and e, and especially from e and d.

Without the alkali metal, its cyanid cannot be formed; and, if it is thus removed from the points Where it is most urgently needed in a continuous furnaceof the class described, if a copious yield of eyanid is to be afforded in the cooling section 3 of the retort, a problem .is presented as to how best to conserve a high content of this metal in zone e.

`If the initial alkalicontent ol' the briquets supplied to hopper S, be too high, then they tend to choke the retort when the latter is operated as in a continuous furnace: this choking or sticking commonly occurring near the entrance to Zone a, which is where the alkali coutent will be highest as a result of the reformation and deposition of the carbonate at this point, as above. describeih-this so deposited carbonate supplementimtIr that already in the briquets. Again, if the rate of feed of the charge through the retort be made excessive, in order to carry alkali metal down to zone n copiously. then (in lhe absence oi heating provisions such as those hereinafter described, or the equivalent thereof), unless the retort he of small diameter. which is obviously objectionable commercially, the charge, which is a poor conductor of'heat, will not all be properly heated by the time in this zone, while substantially preventing cyanid fornaition before this point is reacl1ed,-or, while saidbriquets are trav-` cling toward this point, to preheat them quite uniformly almost but not quite up to the' temperature required for the reaction to occur vlgorouslpY as per equation i, while preserving around them and especially in. their pores, au atmosphere having a relatively high C() content resulting from the cyanid forming reaction therebelow; and

then, in the case Where they are already at reaction temperature byI the time said point is reached, to promptly remore the influence which prevents the formation of cyanid, to permit such formation to take place rigorously.; or, in the case Where the temperature was insufficiently high, to promptly raise this temperature to the degree necessary for copious cyanid formation, while at the same time changing the atmosphere about and in the briquets, to supply one oi' nearly pure nitrogen haring a greatly reduced content.

In other words, While, in the rst instance, the briquets are at a temperature such that iu the absence of the preventing iniiuence, cyanid formation would occur, in the second instance they are insuthciently heated in an atmosphere having but a inoderately high C() content, and since the preferred prei outing influence Lin atmosphere having a decidedy high C() content, the principle in each case is much the same: this principle, of course, involvingr the countering, as it were, of the effect ol higher or lower temperature, by, resper lively, greater or less concentrations of earbon monoxid.

That is to say, I, preferably, either have but a normal development of CO in the upper zones, a and Vb especially, and hold down the temperature while nevertheless thoroughly and uniformly heating the charge at such time; or, I supply an etniasphare particularly high in CO, and depend upon this to blanket down the reaction, so to speak, in spite of the presence of a telnperature sufliciently high to normally yield eyanid copiously.

I may also use a combination of these two applications of the principle in question, by not only supplying, or causing to form, an atnmsphere having a quite high C() content,

uestion is an vi l0 iisA but also Veffecting the indicated heat changes in the different zones of the retortu llfhere avery high carbon monoxid concentration in the upper part of the retort is desired, this can conveniently be acconr plished by piping in hot C() through the pipe 17, to supplement that already present in zones a and I), The velocity of this entering gas is sufficient to project it well down into the retort before it is finally reversed in direction of flow, by the gases ascending toward the hopper 8,

The temperature regulation may be simply and conveniently effected b providing, for cxamplefar'deflecting wallI 4 against which impinge the heating gases traversing the conduit-5g the septum 4 separating conduit 5 from the chamber 6, being pref erably cut away or shaped as shown, t0 cause the gaseous current to pass principally over and around that portion of the retort dei-ined by zones d and e.

VThe Aresult `of this disposition of the gaseous heating current, is'to cause zones b and c, and especially thelatter, to heat up quite uniformly almost, 4but not quite, to

"the desired reaction temperature attained in zone d, especially in the lower part of this zone. and in the up r part of zone e.

The nitrogen flowing up throughthe cooling section 3, becomes highly preheated in sodoing, while, of course, ther descending bri uets in this sectionV are correspondinfrly coo ed, preparatory' .to removal; and t'is current of hot nitrogen should be sufliciently strong to permeate the porous briquets and sweepl out the remaining carbon monoxid carried down in their pores from zones a and b into zone c. This entrained carbon monoxd, by the Way, prevents any very copious formation of cyanid in zonet'.`

As cyanid is largelyK prevented from forming in the npperpart of the heut chamber 'of the` retort, the alkali metal contentof the briquets herein, is preserved in the form of alkali= metal carbonate. Also, since" the rca-'formation of this carbonate near the entrance to zone a is largely prevented,-I

am able to feed through the retort, briquets having a considerably higher alkali metal content, with even less tendency to choke than in the case o briquets having a lower initial carbonate content, where this migrati'on offfalkal metal in the forn of cyanid, is not thus restricted;v "1

'ffceurse,"t some volatiliaation'1of` cyanid wlll occur in zonesd ande; but the amount of this lis relatively small, compared to that which occurs when cyanid is permitted' to i fermV copously'throughout sons, @,'d and,

@,#Whilm on account of the `dovvnvvard movement of the' charge, when operating'` as herein described, even' the alkali metal of d, is qnite'prdmptly returnedto'fzoneconverted lnto carbonate; while,

there said which thus migrates fromV zones e an d (and thereafter to zone 6) following the reconversion osuch cyanid to carbonate in the U() laden zones above.

A further advantage `resides-in thus introducing carbon monoxidgas into the upper zom to supplement the (TO formed during the' cyanidf producing reaction in the lower zone or zones, since, as described in said Bucher Patent No. 1,120,682, the following reaction occurs within the mass of briquets feeding down through the upper end of the retort:

Thus an additional amount of carbon is deposited in especially desirable form, t0- gether with a liberation of heat, directly in the porcs of the briquets being introduced linto the `highly heated portion of the retort.

In Fig. 5 1,120,682, a means for thus introducing carbonmonoxid at the top oi the retort is shown-g but no provision is shown `or described ior simultaneously introducing nitrogen, substantially free from carbon monoxid, :it the lower end of the retort, whereby to sweep away the (1() entrained in theI descending briquctsf-which is obviously most desirable in View ol' the forc- 1 going.

By thus simultancousiy'introducing nitrogen at one end of the retort und carbon inouoxid at the other, as described, I therefore preserve the advantage of obtaining additional carbon for the briquets, with the added advantage that this additional amount of C() is enabled to coact'with the nitrogen current to afford n greater yield of cyanid.

If some carbon dioxid is present in the supply of GU, introduced through the pipe 17, it will, of course, tend to hasten the oxidation of any eya'nid in zone o, or in the portion of the retort immediately thereabove,-with consequent -formation of the carbonate Vat this point; but this is'ot no advantage, since such cyanid is in any ease further since it is desired to effect a conversion of .C0 into CO5, in the space above zone ai, the

presence of this-CO2 is objectionable as tending to retard such conversion to whatever extent the CO, may be present.

To favor the deposition of carbon in the incoming briquets, I prefecto, in effect, prolong that portion of the retort which lies above the zone a., and in order that the temerature in this section may not fall too lbw, which would prevent the desired conversion of C() to 00 I insulate this part of the retort, as Aat 16, etc., to the end that thbriquets in the hopper, or its equivalent, may be maintained at, for example, 550 C. If desired, tlle hopper may belprovided with a removable cover 18, to which may be of said Bucher Patent, No.`

permanently connected that part of the pipe 17 which projects down into section 1 of the retort. The upper part of the pipe is prelerably'scparahly connected to this cover, as is also a closed chute 19, to permit of vertical withdrawal of said'covcr.

Chute 19, forms in effect, an extensin of the retort, so that a 'Further deposition of carbon may be effected therein; but it possesses an advantage over along vertical extension, in that .while the fbriquetstoxbe cyanized may pass freely down thereT through, the inclination of the chute o1' conduit is such as to relieve the plastic mass of briquets in zones a, etc., from the head or pressure that they would otherwise be temperature than ,in diameter subjected to were the chute vertical; while at the same time any necessity for providing moving conveying parts incontact with the hot ascending gases, is eliminated.

I especialy'wish to direct rattention to the variations in temperature in the different zones n, b, etc., which is so conveniently effected in the simple manner shown. effect upon the success of the process, of this provision of a highly heated portion of the retort just above ythe cooling section 3, together with a more moderately heated portion substantially immediately thereu above, is so potent, for reasons hereinbefore set forth, that with it alone and without the provision of the supplementary current of carbon monoxid in the upper zone or zones, it is still possible' to work the retort to advantage. The introduction of additional CO into zone a, however, permits of heating zones a and?) to' a somewhat higher when the pipe 17 is not used, in the fashion described, with the result that the total length of the retort exposed to the action of the heatin gases in chamber 6, ma y be correspon ingly reduced. This favors uniform feeding of the charge and saves retort cost, Vwhich in case the entire retort is of iron, amounts to considerable in time. by reason of the occasional necessar replacements.

I pre er to form the section 2, which is exposed to the more intense heat, of a suitable heat resistant alloy, such as one of nickel, iron and chromium, or the like.

The larger diameter cooling section receives 'the lower end of the alloy section "2, and is welded securely thereto; While I preferably make section 1 of iron, to save expense, and likewise am able-to telescope and weld its lower end into the upper end of section 2 which is correspondingly larger than section 1. Y Another advantage resides in making retort section 1 of less diameter than section 2, since the upward current of gas travers- `mg zones c, b and a is thereby rendered :more rapid than the current of said gas in zones e and d.

The I The effect of this is, that the inflowing nitrogen passing through zones e and' d, does not tend to sweep upward the vaporous cyanid in said zones, which Would increase the undesired volatilization therefrom, as much as would a nitrogen current yof increased velocity; while, on the other hand, the more rapid gaseous current passing through Ifone c, rapidly sweeps out the carhon monoxid entrained in the peres of the briquets descending from zones a and b. i Finally, I desire' to emphasize the im portance of having the hottest part ol the retort as near as possible to the cooling section 3, since it is at thispoint that cyanid i'oiggiation, under the prescribed conditions, ralf occur most copiously, and before such cyanirl has become volatilized to any very matgrial extent, it drops down With the other non-gaseous reaction residues, into the cooling section where, as its temperature is promptly lowered, further volatilization becomes impossible.

To favor this local heating, especially when section 2 isforrned o'f such a heat re. 90 sistant alloy as thatdescribeda convergent apertures 20--20 may be provided in the septum 4, so as to allow a partof the heating gases to pass directly through said wall, preferably at a plurality of points, to permit of impingement of said gases practically against three sides, at least, of the section 2.

The inner wall of this septum may also be` somewhat laterally arched or coned, as shown, to effect a concentration upon section 2 of the heatingr gas descending from the wall In general, therefore, `it will be noted that I have exemplified a plurality of means and modes of procedure 'for retarding the 105 formation of cyanid in or near the end of the externally heated portion of a continuously operating retort, fromwlhich the reaction gases emerge, while especially favoring said formation in 'arreaction zone of hut lim- 110 ited extent compared to the total length of y said heated portion, such reaction zone' being quite closely adjacent tothe cooling section. In the preferred apparatus and mode et conducting thev process, these means and steps are advantageously combined.` to secure economies of apparatus andvuehas well as increased yield of the product sought.

Having thus described my invention, what l claim is: i

l. Apparatus for converting an oxygen compound of an alkali metal into alkali metal cyanid, which comprises a furnace having therein a continuously downwardly feeding retort in an intermediate portion of which the charge feeding through said retort is subjected to heat treatment, said furnace having means for unequally heat ing said intermediate rtion to develop copious formation of said cyanid only well down toward the lower end of said ortion,

while yet graduali and substantia lyjiniformly heatin sai cha e during its downward travel t rough sai intermediate portion toward said lower end, and provisions for abruptly cooling the cyanized charre drectly upon its emergence from said lower end, said provisions including means to introduce a current of nitrogcninto said retort for passage upward through 4said charge.

2. Apparatus for' converting anoxygen compound of an alkali metal into alkali metal cyanid, which comprises a gas-fired furnace having therein a Continuously downwardly feeding retort in an intermediate portion of which the charge feeding through said retort is subjected toheat treatment, said retort having flame directing means for unequally heating said intermediate portion. to develop copious formation of sa'id cyanid only well down toward the lower end of said portion, while yet graduall and substan tially uniformly heating sai( charge Vduring its downward travel thrQughsaid interme diete portion toward said lower end, and provisions for abruptly cooling the cyanized charge directlyupon. its emergence from said lower end, said provisions including means to introduces. current of nitrogen into said retort for passage upward through said charge.r4 y

3. Apparatus for converting an oxygen compound of an' alkali metal into alkali metal cyan'id,'. which'comprises a furnace having therein a retort through which the charge under treatment is substantially continuously delivered, means to heat a part of said retort to reaction temperature, means to establish s; gaseous reactiomhindering blanket around the charge in one end Iof said heated partof the retort, and -means to introduce a urrent' of nitrogen into said retort for passage through lsaid'heated art from the` endthereof opposite that, a ore said toward said first mentioned end.K y

4. combination of a retort in which a ractiois ieffected to produce a, metal eyanid and carbon nonoxid, with; means'to heats'aid retort, a su piementl body of carbon monoxid gas, means toV introduce` said s into said, afagpoint vin the'ltter'lt e temperaturei'of which approinrates that at which said cyandfformingreaction can occur, means to cause movementof the ,v

p'oint in saidlretort, atA

,supply a current of nitro n to said cooling sectlon for movement t erefrom substantially directly into the hottest part of said retort. i

V6. In cyanizing apparatus, the combina' tonof a continuously feeding retort with means for passing a current of nitrogen through said retort in a direction opposite to that in which travels the charge fed through said retort, and means for exteriorly heating a portion of said retort to effect cyanization therein, said vapparatus having provisions for indi-easing the rate of flow ofV said nitrogen during its progress throu h saidfexteriorly heated portion and said eating means having. provisions to most highly heat said retort wheresaid nitrogen -current is flowing relatively slowly therethrough. 7. In cyanizing apparatus, the combination of a furnace comprising a continuously feeding cyanzin retort and means to heat said retort said eating means having provisions to heat an extended portion of said retort but moderately, and to highly heat a succeedin portion of said retort into which the'c arge proceeds from said moderately heated portion, said succeeding portion being of less extent than said first mentioned portion, and said retort having `a cooling section "adjacent said highly heat- -,ed portion 'and' substantially immediatelyv therebeyond in the directionV in which'said charge travels, and means to suppl nitrogen to saldetort `for fixation t ereo'f in said highly heated portion. I t 8. In cyanizing apparatus, a heated continuously feeding retort, in combination with means to heat said retort and means to lio oppositely tothe first mentioned current, nn-

til it is overcome 'and` swept away by said first mentioned current, said gaseous medium establishing an atmosphere unfavorable to cyanid formationfat one end `of said heated portion.`

process :of forming alkali metalt cyanid, which-comprisessubjecting aV-mass containing carbon, alkaliv metal carbonate and catal tic material,`to heat'treatment, while effecting' substantially continuous movement of said mass along a determined path, so regulatingr conditions in' said* mass during said movement as to preserve said carbonate'and substantially prevent formation ofsaid cyanid therefrom, during the grcateripart of said treatment, relatively suddenly 'changing said conditionsto favor the formation of said cyanid, and substan tially directly thereafter cooling thenon 4gaseous products of said reaction to prevent loss of said cyanill by `volatilizatien,

l0. A process of forming alkali metal cyanid, which comprises subjectingr a `mass containing carbon, alkali metal carbonate and catalytic -material, while in the presence of free nitrogen, to heat treatment, while effecting substantially continuous .movement of said mass along a determined path, so regulating,r the temperature of, and the atmosphere around, said mass, during said movement as to preserve Said carbonate and substantially prevent formation of said c vanid therefrom, during the'greater part of said treatment, relatively changing the temperature of said mass and the atmosphere therearound, to favor the formation of said cyanid, and substantially directly thereafter cooling the non-gaseous products of said reaction to prevent loss of said Ycyanid by volatilihation.

l1. lA process of -forming alkali metal cyanid,which comprises subjecting a. mass containing carbon, .alkali metal carbonate Aand catalytic material, while in the presence of free nitrogen, to heat treatment, while effecting Vsubstantially continuous movement of said mass along a determined path, so regulatingr the temperature of said mass during said movement as to preserve said carbonate and substantially prevent formation of said eyanid therefrom during the greater part of said treatment, relatively4 suddenly changing said temperature to favor theformation of said cyanid. and substantially directly thereafter coolingV the nongaseous products of said reaction to prevent loss of said cyanid by volatilization.

1Q. A process of forming alkali metal cyanill. which comprises subjecting a mass containingr carbon.y alkali' metal carbonate and catalytic material. to heat treatment, While effecting substantially` continuous movement of said mass along a ldetermined path,so regulating the atmosphere around said mass during said movement as to preserve said carbonate and substantially prevent formation of said cyanid therefrom, during the greater part of said treatment, relatively suddenly changing said atmosphere to favor the formation of said cyanid, and substantially directly thereafter cooling the :preserve said oxygen com suddenly i non-'gaseous products of said reaction. to prevent loss -of said-cyan'ld by volatihzation. W i 13.v A prodess of forming alkali metal cyanid, which comprises subjecting abulky mass in which is an oxygen'compound capableof actingas the source ofthe alkali metal base of said cvanid, to anatmosphere of nitrogen mixedfpwithcarbon 'monoxid, to und, as such, and prevent itsconversi-on Into said cyanid, while lgradually and substantially unlformly heating successive portions of said mass at a temperature at w ich in the presence of pure nitrogen said cyanid would freely form and volatilize, sweeping away said carbon monoxid from said portions successively, by means of a current of nitrogen while further increasing the tem- -peratureof said portions shcccssively, to promptly form said cyanid copiously, and substantially at once cooling said portions, successively, as they become highly cyanized,',to^ preserve theA cyanid therein and prevent its volatilization.

14. A process of formin alkali metal cyanid, whichcoimprises estab ishing a downwardly moving column of material contain# ing an oxygen compound capable of acting as .the source of the alkali metal base of said .cooling is effected and being established in part by temperature regulation and in part by flowing preheated free nitrogen copiously through said zone to maintain said zone relatively free from carbon monoxid.

15. In a process for fixing atmospheric nitrogen in the form of alkali metal cyanid lby reacting with free nitrogen upon a.

highly porous mixture of carbon, catalytic material and an`oxygen compound of said alkali metal, in a downwardly movingr column of said miirture which is externally heated to effect saidV reaction in an extended intermediate portion of said column and then cooled in a lower part of said column-,the improvement which comprises substantially limiting the seat of said reaction to a zone which is relatively shallow in depth as compared ltothe total length of said externally heated portion, so as to rapidly produce the bulk of the cyanid adjacent said cooled part of the column, and then lowering the temperature of said cyanid, in the upper end ofsaid cooled part,

es rapidly as possible to reduce substantially to .a minimum Athe distillation nf, said' .nitrogen inthe form of 'alkalnmetal cyanid by reactinjr with free nitrogen upon a highly porous mixture of carbon, catalytic material and an oxygen compound of said elkali metal;,= in a downwardly moving column. vof said- .mlxture which is externally heatedfto'4 e'eotl Said reaction in 'an extended intermediate ortion ',of said column and Uhen cooledi i lower part of said column,-the improvement which comprises substantially limiting the seat of said reaction to :a zone which is relatively 4shallow .in Ydepth as compared to the total length of said externally heated portion, in part at least, by .taking advantage of the normally deleterious effect of carbon mom oxid upon' said cyanid, to suppress cyanidr formation except m said zone, said zone being locmtedin Said column immediately above said cooled ,parts and *then lowering the temperature 'of Iseid Acyanid sufficiently to' v'substantially prevent distillation of said cyanii- I 17. In a process for fixing atmospheric nitrogen in fthe forni of :alkali metalcyanid by reacting with free. nitrogen upon a, highly porous mixture' of carbon, catalytic material and an oxygen compound of said alkali ,metal, in a downwardly Imoving column'of said mixture which is externally heated to effect said reaction in an extended intermediate portion of said'column und then cooled in a lower part o *fvseid column,the `im rovement which". comprises substantially limitin the seat 'of said reaction to a zone whic is relatively shallow in depth as compared to the total length of said externally heated portion,- by taking 'advanta of the normally deleterious effect of`car on monoxid upon said cyanid and by temperature regulation, to suppress cyanid formation 4except in Said zone, said zone :being locate in said column immediately above said cooled part,'and then lowering the temperature of said cyanid suiciently to substantially prevent distillation of said cyanid. A

In testimon whereof I have aixed my signature, in t e resence o'f two witnesses.

' C LES P; HIDDEN` Witnesses:

HOWARD C. RIPLEY, HOWARD F. Hmmm. 

